A B-52 Stratofortress launches July 2, 2013, from Andersen Air Force Base, Guam. The Air Force will convert 30 B-52 bombers to a conventional-only role under the New START treaty. (US Air Force)

WASHINGTON — The Pentagon will shrink the number of its nuclear weapon-carrying bomber aircraft and reduce the number of submarine ballistic missile launch tubes as it modifies its force posture to meet the limits of the New START treaty with Russia, the US Defense Department announced Tuesday.

The New START treaty, signed between Washington and Moscow in 2010, sets lower levels for the number of deployed and non-deployed nuclear weapons allowed. Non-deployed status means the delivery system, a bomber, a submarine or an intercontinental ballistic missile (ICBM) launch silo is undergoing maintenance and cannot fire a weapon.

The Air Force will convert 30 B-52 bombers to a conventional-only role, meaning they could not deploy nuclear weapons, a senior defense official said. That will leave the service with 66 nuclear-capable B-52 and B-2 bombers, 60 of which will be in deployed status.

There are 336 ballistic missile tubes on the Navy’s 14 Ohio-class submarines. Four tubes on each of the Navy’s 14 submarines will be converted “so that they cannot be used to launch missiles,” the senior official said. The submarine-launched ballistic missile tube limits under New START are 240 deployed and 40 in non-deployed status.

DoD plans to remove warheads from 50 of its 450 ICBM launch silos, the senior official said. The cuts will be distributed across the Air Force’s three ICBM bases in Wyoming, North Dakota and Montana.

“They’ll be warm, so they’ll be active,” the official said. “They’ll still all be hooked up in their missile fields, but they’ll be empty.”

Four hundred silos will still have nuclear ICBMs inside, the official said. DoD has four additional launch silos that are used for test launches are not impacted by the New START treaty.

The modifications will cost about $300 million over several years, the official said. The reductions must be made by 2018.

The New START treaty also limits the number of warheads on deployed forces to 1,550. ■